1. Field of the Invention
The present invention relates to a heat pipe and a radiating device for radiating heat of an electronic component such as a semiconductor integrated circuit package to the atmosphere.
2. Description of the Background Art
Recently, higher responsiveness and higher integration of an integrated circuit used for electronic devices such as computers have been in greater demand. Accordingly, density of power consumption of an integrated circuit has been increased, and the temperature of the electronic component in operation has been increased. In order to cool the electronic component, a radiating device such as a heat pipe and a heat sink has been used.
FIG. 10 illustrates a heat pipe 2 placed on a semiconductor integrated circuit package 1. A heat pipe is obtained by reducing inner pressure of an air tight container formed by closing both ends of a pipe, and by sealing a little heat carrier such as water or alcohol, which is called a working fluid. At a heated portion of the heat pipe, the liquid turns into steam or gas, the gas radiates heat when it moves apart from the heated portion, and turns into liquid. The liquid returns to the heated portion because of capillary action. The heat is transmitted from the heated portion to the radiating portion by the repetition of this phenomenon.
FIGS. 11A and 11B show, enlarged, a, heat pipe 2, wherein FIG. 10A is a perspective view and FIG. 10B is a cross sectional view.
Heat pipe 2 includes a pipe 3 having a rectangular cross section, a bottom wall 4 closing the bottom portion of pipe 3, and a cap plate 5 closing the top portion of pipe 3. A working fluid 9 serving as heat carrier repeating evaporation and condensation is sealed in pipe 3. A plurality of grooves 10 serving as a passage through which the condensed working fluid returns are formed in the inner wall surface of pipe 3.
FIGS. 12A, 12B, and 12C show a sequence of steps of manufacturing heat pipe 2. As shown in FIG. 12A, cap plate 5 has a column 6 at the center. A through hole 7 is formed in column 6. A working fluid as heat carrier repeating evaporation and condensation is introduced into pipe 3 from through hole 7.
As shown in FIG. 12B, after introduction of the working fluid, the center portion of column 6 is squeezed by a pair of pliers, indicated by arrows causing through hole 7 to be closed. The portion positioned above the crushed portion is cut away from column 6.
Thereafter, as shown in FIG. 12C, the squeezed portion of column 6 is covered by a solder 8 in order to prevent gas leakage.
As shown in FIGS. 11A and 11B, the conventional heat pipe 2 includes column 6 protruding from the top surface of cap plate 5. Although heat pipe 2 functions to radiate heat received from the semiconductor integrated circuit package to the atmosphere, the portion contributing to the radiating function is a length L.sub.0 from the bottom surface of bottom wall 4 to the top surface of cap plate 5. In other words, the effective length of heat pipe 2 is L.sub.0. A length L.sub.1 of column 6 protruding from the top surface of cap plate 5 is a dead length which does not contribute to the radiating function substantially. When considering the space for installing heat pipe 2, it is desired to eliminate the dead length L.sub.1.
When working fluid 9 repeats evaporation and convention, gas pressure in pipe 3 becomes considerably high. The high gas pressure also acts on the crushed portion of column 6. Column 6, having the outer diameter of approximately 1.5 mm, does not have such high strength. Therefore, if the high gas pressure acts on the crushed portion of column 6, the crushed portion sometimes tears. When such a tear is produced, gas in the pipe leaks, carrying out no radiating function.